1. Field of the Invention
The invention relates to an apparatus for retaining two strings of tubulars, and is particularly but not exclusively for use as a spider in the platform of an oil rig and also for use in an elevator of an oil rig. The invention also relates to a device for retaining a string of tubulars the device comprising at least one body part having a curved tapered surface upon which inserts are located for engagement with the string of tubulars.
2. Description of the Related Art
In the formation and operation of oil or gas wells it is desirable to lower a string of tubulars into the well. For this purpose, a retaining device is used in a platform of the rig, known as a spider, and a corresponding retaining device in an elevator of the rig. The string of tubulars is initially retained from falling down the well by the spider. Additional stands of tubulars are moved from a rack to a position above the spider. The stand of tubulars is connected to the string. The device in the elevator is placed around the top of the lengthened string of tubulars. The spider is then released from engagement with the string, and the device in the elevator now takes the full weight of the lengthened string of tubulars. The elevator moves downwardly towards the spider, lowering the lengthened string of tubulars. The spider engages the lengthened string of tubulars and the elevator is subsequently released from engagement therewith. This process is reversed for pulling a string of tubulars out of a well.
It is often desired to lower two substantially parallel strings of tubulars simultaneously, such as a delivery pipe and an injection pipe used in the forced extraction of oil or gas from a well or used in trial wells.
A problem associated with prior art devices is that their construction is large, expensive and can only be used for retaining two strings of tubular.